1. 各部门工资最高的员工

创建Employee 表与 Department 表如下所示，编写一个 SQL 查询，找出每个部门工资最高的员工。例如，根据上述给定的表格，Max 在 IT 部门有最高工资，Henry 在 Sales 部门有最高工资。

-- Employee 表+----+-------+--------+--------------+| Id | Name | Salary | DepartmentId |+----+-------+--------+--------------+| 1 | Joe | 70000 | 1 || 2 | Henry | 80000 | 2 || 3 | Sam | 60000 | 2 || 4 | Max | 90000 | 1 |+----+-------+--------+--------------+-- Department 表+----+----------+| Id | Name |+----+----------+| 1 | IT || 2 | Sales |+----+----------+-- 查询结果+------------+----------+--------+| Department | Employee | Salary |+------------+----------+--------+| IT | Max | 90000 || Sales | Henry | 80000 |+------------+----------+--------+

方案一：判断 e.Salary 是最大值

-- 查询每个部门工资最高的员工SELECT d. NAME Department, e. NAME Employee, e.SalaryFROM Employee eINNER JOIN Department d ON e.DepartmentId = d.IDWHERE e.Salary = ( SELECT MAX(Salary) FROM Employee e WHERE e.DepartmentID = d.ID );

方案二：对每个员工，先统计同部门工资大于他的有几个，这个方法可以筛选出每个部门工资前N高的人

-- 方案二SET @limit_n = 1; -- 定义变量，筛选各部门前N个工资最高的人SELECT d. NAME Department, e. NAME Employee, e.SalaryFROM Employee eINNER JOIN Department d ON e.DepartmentId = d.IDWHERE ( SELECT COUNT(1) FROM Employee e2 WHERE e2.DepartmentID = d.ID AND e2.Salary > e.Salary ) < @limit_n;

2. 换座位

小美是一所中学的信息科技老师，她有一张 seat 座位表，平时用来储存学生名字和与他们相对应的座位 id。 其中纵列的 id 是连续递增的 小美想改变相邻俩学生的座位。 你能不能帮她写一个 SQL query 来输出小美想要的结果呢？ (如果学生人数是奇数，则不需要改变最后一个同学的座位。)

-- 换座位前+---------+---------+| id | student |+---------+---------+| 1 | Abbot || 2 | Doris || 3 | Emerson || 4 | Green || 5 | Jeames |+---------+---------+-- 换座位后+---------+---------+| id | student |+---------+---------+| 1 | Doris || 2 | Abbot || 3 | Green || 4 | Emerson || 5 | Jeames |+---------+---------+

SELECT @cnt:=count(1) FROM seat;SELECT IF(id = @cnt, id, IF(MOD(id, 2)=1 , id+1, id-1) ) id, studentFROM seat ORDER BY id;

3. 分数排名

编写一个 SQL 查询来实现分数排名。如果两个分数相同，则两个分数排名（Rank）相同。请注意，平分后的下一个名次应该是下一个连续的整数值。换句话说，名次之间不应该有“间隔”。

-- score 表+----+-------+| Id | Score |+----+-------+| 1 | 3.50 || 2 | 3.65 || 3 | 4.00 || 4 | 3.85 || 5 | 4.00 || 6 | 3.65 |+----+-------+-- 返回结果（按分数从高到低排列）+-------+------+| Score | Rank |+-------+------+| 4.00 | 1 || 4.00 | 1 || 3.85 | 2 || 3.65 | 3 || 3.65 | 3 || 3.50 | 4 |+-------+------+

SELECT s1.Score, ( SELECT COUNT(DISTINCT Score) FROM Score s2 WHERE s2.Score >= s1.Score ) RankFROM Score s1ORDER BY s1.Score DESC;